Summary: Prostate cancer afflicts 1 in 4 men by the age of 75 and remains a major public health concern in the United States. Despite some success in disease diagnosis and treatment the molecular parameters that influence the transition from prostatic intraepithelial neoplasia to prostate cancer has remained elusive. The long-term goal of our research is to determine the fundamental molecular mechanisms of epigenetic gene transcription in human biology and disease, particularly human prostate cancer. We focus on the role of Polycomb repressive complexes (PRCs) in transcriptional control of the INK4a/ARF locus, gene products of which are the primary mediators of oncogene-induced senescence. PRC-directed gene silencing is mediated by methylation of histone H3 lysine 27 (H3K27me) at target loci in chromatin that is initiated by the lysine methyltransferase EZH2 of the PRC2 and followed by H3K27me association with the PRC1 by binding to chromobox (CBX) proteins, resulting in chromatin condensation and target gene silencing. Our recent study reveals that the silencing activity of PRC1 for the INK4a/ARF locus requires CBX7 interactions with a non-coding RNA transcript ANRIL (the antisense RNA of INK4a locus) and H3K27me via its conserved chromodomain, highlighting a direct role of long non-coding RNA in epigenetic transcriptional silencing. CBX7 and other key components of PRCs that play a key role in cellular lifespan extension by repressing the INK4a/ARF locus are over-expressed in prostate cancer. We further observed in our study markedly elevated expression of ANRIL, CBX7 and EZH2 and a corresponding decrease in p16[Ink4a] expression in prostate cancer as compared to normal prostate epithelial cells. However, the molecular mechanism of non-coding RNA in PRC-directed gene silencing is not clear. In this project, we aim to determine the molecular underpinning of the functional interplay between non-coding RNA and H3K27me in gene silencing by the PRCs in normal prostate epithelial cells, as well as during the conversion of prostatic intraepithelial neoplasia into prostate carcinoma using combined chromatin/cell biology and structural/chemical biology methods. We expect that the results emerging from our studies including novel chemical tools will have profound impact on a better understanding of prostate cancer biology and future advance of therapeutic means for prognosis and prevention of human prostate cancer.